docs: def is_enrolled(self, experiment_name, alternative):
          """Enroll this user in the experiment if they are not already part of it. Returns the selected alternative"""
          """Test if the user is enrolled in the supplied alternative for the given experiment.
  
          The supplied alternative will be added to the list of possible alternatives for the
          experiment if it is not already there. If the user is not yet enrolled in the supplied
          experiment they will be enrolled, and an alternative chosen at random."""
          chosen_alternative = self.enroll(experiment_name, [alternative])
          return alternative == chosen_alternative